1. Field of the Invention
This invention relates generally to earth boring tools.
2. Description of the Related Art
Earth boring tools are commonly used to bore through a formation to form a borehole. Such boreholes may be formed for many different reasons, such as drilling for oil, minerals and water. One type of earth boring tool is a rotary earth bit. Several examples of rotary earth bits are disclosed in U.S. Pat. Nos. 3,550,972, 3,847,235, 4,096,917, 4,136,748, 4,427,307 and 4,688,651 4,741,471 and 5,358,061. A rotary earth bit generally includes one or more lugs coupled together to form an earth bit body, wherein the lugs include a lug journal positioned towards a lower portion of the corresponding lug. The rotary earth bit includes a cutting cone rotatably mounted to a corresponding lug journal to form a bit bearing cavity therebetween. The cutting cone is rotatably mounted to the lug journal using ball and roller bearings. One or more bit seal assemblies are positioned to hold lubricant in the bit bearing cavity to facilitate the rotation of the cutting cone about the lug journal.
In operation, the rotary earth bit is operatively coupled to a drill string, and moved downwardly through the formation and rotated to form the borehole. As the rotary earth bit moves downwardly and rotates, the cutting cone engages the formation and rotates about the lug journal in response. Debris flows towards the bit bearing cavity in response to the rotary earth bit being moved downwardly through the formation. Debris in the bit bearing cavity restricts the ability of the cutting cone to rotate about the lug journal. The debris can be of many different types, such as cuttings, water and/or mud.
Another type of earth boring tool is a raise boring reamer assembly. Several examples of raise boring reamer assemblies are disclosed in U.S. Pat. Nos. 3,220,494, 4,042,047, 4,053,244, 4,071,098, 4,142,598, 4,179,000, 4,191,267, 4,194,578, 4,228,863, 4,270,618, 4,301,876, 4,386,670, 4,456,082, 4,697,652, 4,832,135, 5,199,510, as well as U.S. Patent Application No. 20050252693 and International Application No. PCT/SE2003/000433.
A raise boring reamer assembly includes a raise boring body which carries one or more cutter assemblies. The cutter assemblies are positioned towards an upper portion of the raise boring body. In a typical set-up, the cutter assembly includes a saddle carried by the raise boring body, and a cutter rotatably mounted to a journal assembly to form a cutter bearing cavity therebetween. The journal assembly is mounted to the saddle in a repeatably removeable manner, and the cutter is rotatably mounted to the journal assembly using ball and roller bearings. One or more seal assemblies are positioned to hold lubricant in the cutter bearing cavity to facilitate the rotation of the cutter about the journal assembly.
In operation, the raise boring reamer assembly is operatively coupled to a drill string, and moved upwardly through the formation and rotated to form the borehole. As the raise boring reamer assembly moves upwardly and rotates, the cutter engages the formation and rotates about the journal assembly in response. Debris flows towards the cutter bearing cavity in response to the raise boring reamer assembly being moved upwardly through the formation. Debris in the cutter bearing cavity undesirably restricts the ability of the cutter to rotate about the journal assembly. Hence, it is desirable to restrict the ability of debris to flow to the cutter bearing cavity, and to move debris away.